A conventional self-ballasted fluorescent lamp typically includes a luminous tube, a cover, a lighting device, and a globe. The luminous tube has bent bulbs. A base is fitted to one end of the cover, and the luminous tube is supported at the opposite end of the cover. The lighting device is disposed inside the cover. The globe is attached to the other end of the cover and encases the luminous tube.
There is a conventionally known example of a self-ballasted fluorescent lamp, as disclosed by Japanese Laid-Open Patent Publication No. 2004-55293, which is hereby incorporated by reference in its entirety herein. In this self-ballasted fluorescent lamp, the tip of a thin tube extruding from an end of a bulb of a luminous tube is extended into a base, and an amalgam for mercury vapor pressure control is sealed in the tip of the thin tube. This configuration is capable of maintaining a relatively low temperature at the tip of the thin tube even during lighting and enables an increase in mercury vapor pressure regardless of the temperature conditions when the lamp is not lit. As a result, luminous flux rising characteristics immediately after lighting is improved. This lighting device has a substrate disposed so as to extend in the direction intersecting the height of the lamp, and the distal end of large-size electronic components that protrude higher than do other electronic components mounted on the substrate are positioned, together with the thin tube, inside the base.
Although self-ballasted fluorescent lamps having such a configuration as described above are becoming more compact recently so that their lamp length and maximum outer diameter are similar to those of electric light bulbs for general illumination as defined by JIS Standard, the cover of those conventional self-ballasted fluorescent lamps for housing the lighting device has a considerably large maximum outer diameter or occupies a proportionally large part of the lamp length. Such a large cover not only makes it difficult to bring the appearance of the self-ballasted fluorescent lamp sufficiently close to that of an electric light bulb for general illumination but also blocks a large proportion of light distribution to the side where the base is provided. As a result, during the time the luminous tube is lit, light distribution characteristics are not sufficiently similar to those of an electric light bulb for general illumination.
There is another conventionally known example of a self-ballasted fluorescent lamp, as disclosed by Japanese Laid-Open Patent Publication No. 2004-165053, which is hereby incorporated by reference in its entirety herein. In this self-ballasted fluorescent lamp, a substrate of a lighting device housed in a cover is positioned vertically along the height direction of the lamp; a narrow portion that enables insertion of the substrate along the center axis of the base is formed at the base-facing end of the substrate; and the narrow portion and a part of the electronic component mounted on the narrow portion are disposed inside the base.
As described above, although the appearance of conventional self-ballasted fluorescent lamps is becoming increasingly similar to that of an electric light bulb for general illumination, their dimensions are not sufficiently similar to enable replacement of an electric light bulb for general illumination without causing any negative aspects.
It is possible to make the cover compact by positioning the substrate vertically so as to enable the narrow portion of the substrate and a part of an electronic component to be placed inside the base, thereby reducing the size of the portion of the substrate that is located in the cover but outside the base. However, as the narrow portion of the substrate is positioned along the center axis of the base, the maximum distance between each of the two faces of the substrate on which electronic components are mounted and the part of the inner wall of the base facing the substrate face is ½ of the maximum width of the space inside the base (in cases where the cylindrical portion of the cover protrudes into the base, the maximum width of the internal space of the cylindrical portion), and the height of each electronic component to be mounted is limited within such a range as to permit positioning in such a space. Therefore, electronic components, such as a choke coil, that protrude a substantial distance from the substrate and cannot be positioned in the base have to be provided outside the base. Furthermore, an electronic component having a greater height, such as a smoothing capacitor, has to be mounted with its lead wires at an approximately right angle so that they extend along the substrate in order to reduce the height of the electronic component, i.e. the distance by which the electronic component protrudes from the substrate. However, doing so increases the area on the substrate occupied by the electronic component, resulting in the need for a larger substrate.
In short, merely positioning the substrate vertically and providing a narrow portion of the substrate and a part of an electronic component in the base does not enable efficient positioning of the lighting device in the base or the cover to be made sufficiently compact. Furthermore, it is difficult to give the lamp an appearance sufficiently similar to that of an electric light bulb for general illumination.
A self-ballasted fluorescent lamp with a thin tube positioned inside the base as offered in Japanese Laid-Open Patent Publication No. 2004-55293 does not enable a component to be positioned in the space inside the base with sufficiently high efficiency, because the thin tube is positioned close to the distal end of a large-size electronic component. As the electronic components must be mounted on the substrate in such a manner as not to come into contact with thin tube, this configuration presents limitations in how much the component placement efficiency can be increased. It is difficult to make the cover compact, because the substrate, which is positioned between the base and the luminous tube, is inevitably larger than the base.